1. Technical Field
The embodiments herein generally relate to a LADAR transmitting and receiving apparatus, and, more particularly, to a compact LADAR transmitting and receiving apparatus provided at a reduced cost and with reduced power requirements.
2. Description of the Related Art
Laser Detection And Ranging (LADAR) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. LADAR may be used in a variety of contexts for elastic backscatter light detection and ranging (LIDAR) systems. Although the acronym LADAR is usually associated with the detection of hard targets and the acronym LIDAR is usually associated with the detection of aerosol targets, there has been no real standard on their use and both acronyms may be used interchangeably to describe the same laser ranging system.
While a LADAR system may perform similar functionality to a radar system, LADAR uses a much shorter wavelength of the electromagnetic spectrum compared to radar. For example, LADAR systems typically operate in the ultraviolet, visible, or near infrared spectrums. This gives a compact LADAR the ability to image a target at a high spatial resolution and allows LADAR systems to be made more physically compact.
In order for a LADAR system target to reflect a transmitted electromagnetic wave, an object needs to produce a dielectric discontinuity from its surroundings. At radar frequencies, a metallic object produces a dielectric discontinuity and a significant specular reflection. However, non-metallic objects, such as rain and rocks produce weaker reflections, and some materials may produce no detectable reflection at all, meaning some objects or features are effectively invisible at radar frequencies.
Lasers provide one solution to this problem regarding non-metallic detection. The beam power densities and coherency of lasers are excellent. Moreover, the wavelengths are much smaller than can be achieved with radio systems, and range from about 10 μm to around 250 nm. At such wavelengths, the waves are reflected very well from small objects such as molecules and atoms. This type of reflection is called diffuse “backscattering.” Both diffuse and specular reflection may be used for different LADAR applications.
The transmitter and receiver functions (transceiver) of current LADAR systems typically rely on a mono-static optical system (i.e., the transmitted and received beams are co-axial) that is a complex assembly of beam splitters, polarizers, and steering mirrors. This arrangement is generally expensive, very difficult to align, prone to losing alignment, subject to narcissus, and requiring much more space than desired for a compact LADAR system.
In addition, current compact LADAR systems have generally been flawed by one or more factors including, low pixelization, insufficient range or range resolution, image artifacts, no daylight operation, large size, high power consumption, and high cost. Current LADAR systems frequently use a wide bandwidth photo detector/amplifier system with a small detector, and a low shunt capacitance, leading to an undesirable signal-to-noise ratio.